It is well known in motor vehicles to provide a metal substructure and to mount a decorative plastic outer body panel on the metal substructure to define the outer appearance surface of the vehicle body. The use of such plastic panels is desirable in order to obtain vehicle design goals such as weight reduction and corrosion resistance. Furthermore, relatively soft and flexible plastic body outer panels offer a lessened susceptibility to damage from minor impact.
A shortcoming of the use of plastic body outer panels to define the outer appearance surface of a motor vehicle body is that the plastic panel cannot be welded to the adjacent panels or to the underlying metal substructure. Furthermore, the attachment of the plastic panel to the metal substructure can result in highly visible surface distortion of the plastic panel unless the plastic panel is mounted on the substructure in a precise manner in which the relatively flexible plastic panel is not twisted or bent.
The challenge of mounting a plastic panel upon the metal substructure is further complicated by the fact that the plastic panel and the metal substructure have substantially different rates of thermal expansion. Furthermore, plastic panels are known to have a high rate of hygroscopic growth causing the plastic material to grow substantially in dimension under conditions of high humidity.
When the plastic panel is mounted on the metal substructure by conventional screw or rivet type fasteners, the thermal and hydroscopic growth of the plastic panel causes the panel to exhibit highly visible surface distortion characteristics such as bulges and ripples.
It would be desirable to provide an attachment of a plastic outer body panel upon the body substructure by a device and in a manner which enables thermal and hygroscopic growth of the plastic panel while permitting the body outer panel to preserve a distortion-free appearance.
Furthermore, it would be desirable to provide a plastic panel mounting device and method by which the plastic panel is mounted on the metal substructure in a manner which precisely aligns and spaces the plastic panel with the adjacent plastic panels irrespective of manufacturing tolerance and dimensional variation in the metal substructure.